Since the 1970s, the cost of energy and the public awareness of the negative environmental effects of unrestrained energy consumption have increased worldwide. One of the largest components of humankind's total energy consumption is internal climate control—mainly, heating and cooling—of residential, commercial, and public buildings. An effective way to reduce this consumption is thermal insulation of building shells, such as exterior walls and roofs, since most of the energy used in controlling internal temperature compensates for the flow of heat from or into the building.
It is generally known that the best insulator against heat transfer by conduction and convection is vacuum. This concept has been put in practice in the form of the vacuum insulation panel (VIP) which typically comprises an evacuated, hermetically sealed, and approximately rectangular prismatic enclosure of low thickness/width and thickness/length ratios, having walls made of a high-barrier film or foil, and containing an internal rigid or semi-rigid core that keeps the walls from collapsing together under atmospheric pressure. The film is designed to keep diffusion of atmospheric gases, including water vapor, through it at an extremely low level, so that an effective internal vacuum can be maintained inside the VIP for many years. Thermal resistance (R value) equal to or greater than 50° F.·ft2·h/Btu (degrees Fahrenheit—square foot—hour per Btu) has been achieved commercially.
Thermal resistance, designated as “R” or “R value”, is a well-known quantity in the insulation industry. It typically pertains to heat transfer per unit area across the thickness of a planar or nearly planar insulating panel. As with electrical resistance, the thermal resistance (R value) of a stack of insulating panels equals the sum of the individual R values of the panels. The R value of a panel is defined as the ratio of the temperature difference ΔT (delta T) between the two sides of the panel to the steady-state heat flux Q/A:
  R  =                    Δ        ⁢                                  ⁢        T                    Q        ⁢                  /                ⁢        A              =          1      U      where Q is the total heat flow (in units of Btu/h or Watts, for example) through a planar area A (square feet or square meters, for example). Thermal resistance R is the reciprocal of another well-known quantity, the overall heat transfer coefficient U.
In the United States, the most commonly used unit of R is ° F.·ft2·h/Btu. The conversion factor to the corresponding SI unit is:0.1761 (K·m2/W)/(° F.·ft2·h/Btu)
Although VIP's have been used successfully in refrigerators and aerospace applications, they have not penetrated the building construction and remodeling market significantly. One reason has been that their gas barrier enclosure is easily torn or punctured during transport to, or installation at, a job site. The general concept of sandwiching the VIP between rigid protective boards to make what we call henceforth an “insulating composite panel” (ICP) has been proposed to address this problem. However, the prior art has not evidenced a practical implementation of the concept for use as an insulating component in roofing, where special fitness for use requirements must be met, for example:                1. fire resistance,        2. mold resistance,        3. light weight per unit area, and        4. wind uplift resistance.        
Requirement 1 is a safety issue, usually legislated by building codes. Requirement 2 is a sanitary issue involving the growth of fungi generally known as mold and mildew. Requirement 3 meets builders' need for ease of hauling and assembling roofing elements on a high roof during construction. Requirement 4, which is also usually part of building codes, merits explanation.
Wind uplift is a well-known phenomenon in the roofing industry. It is a consequence of Bernoulli's law, which states that an inviscid (zero-viscosity or, in practice, low-viscosity) fluid moving simultaneously past two opposite surfaces of a solid body at different speeds generates a net pressure pushing the body towards the high-speed side. This is the principle behind the uplift on airplane wings. In the case of a roof, the air speed under it (inside the building) is essentially zero, but the air speed over it (outside the building) can be very high when there is a storm. Therefore, there can be a large pressure difference pulling roof components, including insulation panels, upwards, and in extreme cases, causing them to fly away. Combining Bernoulli's law with the ideal gas law, the formula approximately quantifying this pressure difference is obtained as:
            v      out      2        -          v      in      2        =                    2        ⁢        RT            M        ⁢          ln      ⁡              (                              P            in                                P            out                          )            where ν is the air velocity near the roof (m/s), R is the universal gas constant=8314 J/Kmol·K (Joules/Kilo-mole·deg Kelvin), T is the absolute temperature (degrees K), M=28.8 kg/Kmol is the average molar mass of air, P is absolute pressure (any unit), the subscripts “in” and “out” denote the side of the roof inside and outside the building, respectively, and ln is the natural logarithm. In most practical cases, νin is about 0, and Pin is close to 1 atm=2117 lbf/ft2. With appropriate unit conversions, and setting T=10° C.=50° F.=283K, the following representative results are calculated:
voutmi/h0108153188218245Pin-Poutlbf/ft20306090120150Noting that Pout is less than Pin which is normal atmospheric pressure, the positive pressure difference Pin−Pout is defined as the “wind uplift pressure”. As can be seen, with wind gusts of 100-200 miles per hour (mi/h) typical of tornados or hurricanes, there can be substantial uplift force on the roof, at least for a few seconds.
The applicant's review of the prior art did not reveal references that fully address means or method for meeting important roofing requirements such as those listed above. A discussion of the prior art follows:
In a conference paper published in 2009, Musgrave describes an ICP consisting of a VIP sandwiched between two rigid “skins”, with adhesive between skin and VIP on either side. (D. Musgrave, “Structural Vacuum Insulation Panels”, International Vacuum Insulation Symposium, Session 2A, London, UK, 2009.) This paper focuses entirely on the thermal and structural advantages of such an ICP. This becomes apparent in the specific materials suggested for the skins, which consist of those mentioned in the following passage, quoted verbatim from the paper: “The skins can be almost any material such as steel, aluminum, or composites. If the skins are composite sheets, it can cover the full range of composites from common fiberglass reinforced polyester thermo-set resin to carbon fiber in an epoxy resin. Some extremely high grade composites are almost 3 times the modulus (stiffness) of steel.”
In German patent application DE 10 2009 054 432 A1 (also published as EP 2,504,501) by Schröer et al., FIGS. 6 and 8 show an ICP consisting of a VIP sandwiched between upper and lower protective sheets. Although a variety of possible materials are casually mentioned for these sheets, their purpose beyond protecting the VIP from puncture or tearing is not considered. The patent application is focused on the method of attaching the ICP to rafters or a roof deck. This is achieved by means of screws or nails going through a “helper slat” (“hilfslattung” in German) interposed between adjacent VIPs and attached to the protective sheets. An obvious disadvantage is that non-VIP material, especially multiple panel-length strips such as these “helper slats” provide each panel with a significant proportion of area having a path of higher thermal conductivity through which heat flow can circumvent the VIPs.
In Chinese patent CN 201486072 assigned to Chengdu Somo Nanotechnology Co. LTD, as best as can be determined from the single drawing plus a rough machine translation, a VIP is shown encased completely in plaster, and described as having a total thickness of 15 mm. Allowing for a reasonable thickness for the VIP, this indicates that each of the two plaster layers covering the larger surfaces of the VIP is very thin and, therefore, fragile. Furthermore, plaster tends to absorb moisture and is vulnerable to mildew. It appears that the disclosed object is designed for use as a relatively small indoor ceiling tile.
In the international patent application publication W02005/068917 by Hake, the VIP (23) is totally encased in a hard-sided box or “cassette” (7) made of sheet metal, plastic, or wood. The box provides structural strength to the insulation portion (3) of a large self-supporting structural building component, and is shown being installed in cooperation with many different roofing elements. Hake's design approach is very specific to his objective of providing a large self-supporting structural building component suitable for installation on spaced-apart rafters. It can be seen that for installation on a flat roof, Hake's large, totally enclosed VIP component would be unnecessarily expensive, heavy and awkward to handle. Furthermore, the (vertical) cassette walls between adjacent VIPs obviously create a non-uniform R value over the roof as a whole, due to the low R value along every line of cassette walls.
The international patent application publication W02013/025272 by Castelle discloses a series of interlocking evacuated canisters—not panels—made of a malleable rigid material such as aluminum sheet. In many ways, Castelle's concept appears to be inappropriate for use as a roofing panel. For example, the materials may be inherently mold and fire resistant, but these metallic canisters are meant for insertion into hollow walls, and are not designed to resist wind uplift on a roof. For example, air gaps and metal walls between canisters would be vertical instead of horizontal when laid on a roof, thereby providing a low R value pattern due to convection as well as conduction.
In U.S. patent application U.S. 2003/0082357, Gokay et al. disclose a VIP design that includes heat-resistant sheets surrounding a vacuum supporting core structure such as a polymeric foam, which is heat-sensitive. The sheets and core are all inside the VIP membrane enclosure. Thus Gokay only discloses a VIP structure, not an insulated composite panel (ICP).
In European patent EP 1,213,406, Schnös describes a wall insulation system assembled at the construction site, comprising a VIP propped against a pre-existing vertical wall, supported by wall-mounted channel-shaped profiles on its four thin sides, and covered on its remaining large side by a cover panel of gypsum board, expanded polystyrene, or wood, attached to the profiles. There is only one cover board, and the VIP is not adhered to it or to the wall. It is unlikely that the wind uplift requirement would be met if this system were installed on a sloped or flat roof.
Given the obvious limitations and inadequacy of the above-described prior art, all of which relates to aspects of an ICP incorporating a VIP, it is an objective of the present invention to devise an ICP design that fully addresses roofing requirements such as the four listed above.
Beyond meeting minimum requirements, it is an objective to determine specifics of a premium insulated roofing system of materials and method sufficient to produce a finished roof with a very high R value but minimized thickness, and having durability for a long effective life.
Even further, it is an objective to simplify and minimize the cost of the ICPs and their installation, while maximizing the R value uniformity and coverage of the roof.